The present invention relates to hydraulic power supplies, and more particularly to air operated volumetric hydraulic power units ideally suited for powering high production multiple head welding machines and like equipment.
Machines using fluid motors (e.g., piston and cylinder assemblies) to drive working pistons for clamping tools, actuating tools or welding guns, etc. are generally either pneumatically or hydraulically powered. If high speed is required air is often preferred because it is cleaner and will give faster action than oil at the same supply pressure; however, saftey limits on usable pressures result in cylinder sizes which are too large for many applications. Oil can be used at higher pressures, thereby reducing cylinder sizes, but to get fast action relatively large displacement pumps are required. Hydraulic power units therefore tend to be large and costly, and because they have continuously operating pumps (even during the dwell or rest portion of the load cycle, because they must be able to quickly meet any sudden demand) they consume substantial amounts of power (variable displacement pumps may consume only moderate power, but are even more costly) are a source of continuous noise, and generate considerable heat because all excess is dumped back to the reservoir after being raised to working pressure.
It is therefore a primary object of this invention to provide an improved hydraulic power supply which operates on demand only, i.e., it supplies oil under pressure only when required by the load, thereby virtually eliminating the consumption of power (and attendant operating cost), noise and heat build-up when the load is in the dwell or rest part of its cycle (often a substantial proportion of the total cycle time). A related object resides in the provision of unique reset means for insuring full completion of each cycle of the power unit prior to initiation of a new cycle.
Further objects of the present invention concern the provision of a demand type hydraulic power unit which can be easily sized for any volumetric demand, which is relatively compact and economical, which can provide desired high speeds without requiring bulky and costly accumulators, and which can be retrofit to existing machines.
Another object of this invention resides in the provision of a demand type hydraulic power unit which optionally can provide an intensified output for those applications where a two-stage advance stroke is desired, i.e., one in which the hydraulic piston initially advances toward the workpiece at a high rate of speed but with relatively little force, and upon engagement with the workpiece provides very high force but with limited displacement.
A further object of this invention resides in the provision of an auxiliary hydraulic power unit coupled with the primary power unit which discharges intensified oil during the return pressurized function of the primary power unit to lock up retract oil in the return machine manifold to keep the rod ends of the working pistons from drifting downward when the fluid motor is shut down for a period of time (and pistons are mounted with rod ends down) and also intensify return oil to retract end of working piston (when stuck due to bent rods or the like).
A further advantage of the present invention is that in one embodiment fluid is returned to a hydraulic slave cylinder under pressure (and not through a reservoir) for a faster refill caused by the back pressure of the unit and thereby faster cycling of the unit.
In some instances, fewer hydraulic working pistons may be used and less air is necessary to drive the power unit. In such cases, a significant cost advantage occurs if the working volume of the master cylinders are diminished. It is a further advantage of the present invention to provide a simple and efficient means of reducing the working volume of the master cylinders as desired to attain a cost savings using less pressurized air when fewer working pistons than the maximum number are utilized.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.